Therapy For Chemotherapy-induced Peripheral Neuropathy.
Published 2013 · Medicine
In Reply Drs Abbott and Zee comment on the possibility of lower urinary melatonin levels serving as a marker for underlying circadian misalignment related to cumulative shift work. We have also contemplated the possibility that melatonin levels are simply a reporter of circadian alignment rather than a marker for abnormal glucose metabolism. Melatonin levels among individuals in the NHS have been shown to be inversely associated with the number of night shifts performed in the 2 weeks preceding the measurement,1 whereas no association was found between melatonin levels and the total number of years of previous shift work for individuals in the NHS.2 This suggests that shift work likely does not have a sustained effect on melatonin secretion. Additionally, the association of increased shift work with increased risk of incident type 2 diabetes shown in the NHS cohort appeared to be largely mediated by increased body mass index,3 whereas the association of melatonin with incident type 2 diabetes in our study was independent of body mass index. Nevertheless, we think that Abbott and Zee raise an important issue about the relationship between other forms of chronic circadian misalignment and melatonin secretion. If the low levels of nocturnal melatonin secretion within our cohort were indeed attributable to circadian misalignment due to factors other than prior or current shift work, then the association between low melatonin secretion and incident type 2 diabetes could simply represent an association of circadian misalignment and incident type 2 diabetes. Careful studies are needed to delineate which circadian intervention may be suited to beneficially affect glucose metabolism and whether melatonin levels are a modifiable risk factor.